The disclosure relates to a rotating control device used in a drilling system having a non-rotating tubular RCD housing enclosing an elongate passage. A mandrel rotatably extends along the passage about an axis. A seal assembly seals the RCD housing to the mandrel and provides first and second seals against the mandrel's exterior surface. The first and second seals are spaced parallel to the mandrel's axis to create space between the mandrel and the first and second seals. The first seal has a first side exposed to fluid pressure in the RCD housing and a second side exposed to fluid in the space between the seals. The second seal has a first side exposed to fluid pressure in the space between the seals and a second side exposed to fluid pressure at the exterior of the RCD housing. A pressure stepping mechanism supplies fluid to the space between the two seals.